纳米氧化锡粉体制备研究进展

纳米二氧化锡粉体是一种重要的气敏、湿敏、压敏基体材料。文章系统介绍了近年来不同方法制备纳米二氧化锡粉体的过程、原理和制备条件,描述和分析了目前各种制备超细二氧化锡的方法和特征及各方法的优缺点,并对其应用前景做出了进一步的展望。     

氧化共沉淀制备锑掺杂超细SnO2的工艺探讨

研究了用氧化共沉淀方法制备掺锑纳米二氧化锡粉料的适宜工艺条件，探讨了前驱体的快速洗涤分离。结果表明：通过降低前驱体的溶剂化作用，可促使胶粒聚集，从而可有效加快洗涤分离前驱体的速度。可以解决使用沉淀法制备超细(纳米)粉体过程中存在的沉淀难以洗涤分离的弊端，为工业上利用沉淀法制备掺锑纳米SnO2粉体创造了条件。     

自蔓延高温合成高熔点粉体的研究现状与发展

自蔓延高温合成(SHS)技术是制备高熔点化合物材料的有效方法之一,其具有低能耗、高效率等特点。自蔓延高温合成技术是利用反应体系中自身放热来引发并维持反应的进行。自蔓延高温合成技术在制备粉体材料上应用广泛,并且结合了"化学炉"以及机械诱导等手段提高了合成过程中的效率,目前人们已经通过这种技术制备了硅化物粉体、碳化物粉体、氮化物粉体以及硼化物粉体等,所得产品具有较高的致密度以及较小的颗粒尺寸。目前,二元系高熔点化合物的研究已经基本成熟,而三元系高熔点化合物的研究尚未深入展开。综述了国内外自蔓延高温合成技术在高熔点化合物材料制备上的应用与发展,在总结了二元系自蔓延高温合成技术的基础上进一步总结了三元系高熔点材料的合成,并讨论了现有自蔓延高温合成技术的不足与未来发展趋势。     

高纯超细电子陶瓷粉体材料的制备

概述高纯超细电子陶瓷粉体材料的主要制备方法，详细阐述了固相法，液相法和气相法的原理与特点及国内陶瓷粉体材料生产情况。     

高纯超细电子陶瓷粉体材料的制备

概述高纯超细电子陶瓷粉体材料的主要制备方法，详细阐述了固相法，液相法和气相法的原理与特点及国内陶瓷粉体材料生产情况。     

钛酸锶粉体的共沉淀法制备研究

钛酸锶是电子工业用重要原料,试验采用化学共沉淀法制备钛酸锶粉体,选用碳酸钠和氢氧化钠作为沉淀剂,初始原料采用氯化锶和四氯化钛溶液,重点研究了反应物锶钛比、终点p H值、固液分离物的洗涤以及煅烧温度等共沉淀法合成钛酸锶的条件,并进行了分析测试,结果表明,制备的钛酸锶粉体具有颗粒平均粒径小,晶型完整,产品纯度高的特性。     

非晶半导体薄膜用Te系化合物靶材制备

采用真空熔炼法, 经急冷和缓冷两种不同冷却条件制备了Te系化合物TeAsGeSi合金粉体.通过X射线衍射分析, 急冷工艺制备粉体呈非晶态, 缓冷工艺制备的粉体呈晶态, 结晶主相为R-3m空间群的As₂GeTe₄; 差热-热重分析显示, 升温至350℃时缓冷粉体As₂GeTe₄成分熔融, 400℃时两种粉体均开始快速失重, 为避免制备过程中发生材料熔融及挥发损失, 确定烧结温度不超过340℃.采用真空热压法制备TeAsGeSi合金靶材, 将两种粉体分别升温至340℃, 加压20 MPa, 保温2 h制备出两种靶材, 其中缓冷粉体制备的靶材致密度高, 为5. 46 g·cm-3, 达混合理论密度的99. 5%, 形貌表征显示此靶材表面平整, 孔洞少, 元素分布均匀.      

镁铝尖晶石粉体的性能、制备与应用趋势

近20年来,镁铝尖晶石制备技术及应用发生了根本性变化.过去用于耐火材料、耐磨材料、陶瓷工业的镁铝尖晶石粉体,逐渐应用于功能材料、激光晶体材料等高技术领域.综述了高性能镁铝尖晶石的性能、以及制备技术的发展状况和应用前景.特别指出粉体纯度是一个重要性能指标.     

高折射率镀膜材料LaTiO3

高稳定高折射率光学镀膜材料是应用光学发展的迫切需求.直接采用TiO2和La2O3粉体为原料, 低成本制备了单相LaTiO3高折射率光学镀膜材料.利用该LaTiO3材料制备的薄膜在折射率、色散、消光系数等方面表现出良好的性能, 多层高折射率膜的反射率也很低, 批次稳定性实验表明该材料具有良好的稳定性.因此, 该单相LaTiO3材料具有好的推广应用前景.     

氮化铝粉体制备技术的研究现状与展望

阐述了氮化铝粉体可作为新型高热导率基板材料原料的理由.对国内外AIN粉体制备技术的特点和研究进展进行了综述,对氮化铝粉体的制备技术进行了展望.     

本钢X70管线钢的组织与性能

介绍了本钢开发研制的X70管线钢化学成分和生产工艺特点,并对其组织性能进行了分析.结果表明,本钢X70管线钢具有高强度、高抗动态撕裂能力、高低温冲击韧性以及低韧脆转变温度.其优良的性能得益于内部具有与细小析出相交互作用的高密度位错的超低碳针状铁素体组织.目前已形成批量生产能力.     

DT碳化钨钢结硬质合金显微组织结构的研究

通过对DT合金各相的成份、形貌、结构特点的观罕及热处理工艺对其影响的分析,揭示出该合金的显微特征,并就进一步提高合金性能从理论上进行了初步探讨。碳化钨相与基体相在加热到高温时发生相互溶解和扩散。各元素的分布有一定的规律。扩散的结果强化了两相的结合。碳化钨相存在溶解、析出和长大倾向不同的两种颗粒,它们的形貌和成份均不同,一种是W向基体扩散较多、外形已明显"球化"的颗粒;另一种是W向基体扩散较少,外形尚未明显"球化"的颗粒。通过比较认为:若能使合金中碳化钨相颗粒实现"球化,"可能有利于提高性能。固溶有其他元素的碳化钨相仍保持WC的结构类型,但晶格常数大于WC,而且随回火温度提高,晶格常数a和c减小。     

高饱和磁化强度Fe_3O_4纳米粒子的制备及表征

实验采用反滴定化学共沉淀工艺在无任何惰性气体保护情况下合成了纯度高、结晶性好的四氧化三铁纳米粒子,测试结果显示,其饱和磁化强度高达104．6emu／g。用X射线衍射仪、扫描电镜、选区电子衍射和X射线光电子能谱表征了四氧化三铁纳米粒子的形貌结构及化学成分等性质,用振动磁强计测试其磁性质。详细的讨论了pH值、陈化温度、陈化时间等因素对磁性质的影响机制。     

Characteristics of Ti‐Ce Complex Deoxidation Products in a Fe‐20mass%Cr Alloy

The particle characteristics such as size distribution, composition and morphology have been studied in an Fe‐20mass%Cr alloy as a function of holding time at 1600°C. The alloy was deoxidised with Ti and Ce, followed by holding at 1600°C and cooling to 1400°C and quenching. The inclusion particles were investigated on a surface of film filter with an open pore size of 0.05 or 5 μm after electrolytic extraction of the metal samples. Different electric charge and electrolytes (2%TEA and 10%AA) were compared for extraction of the Fe‐20mass%Cr alloy. 300 Coulombs with 10%AA was found most suitable for the electrolytic extraction of particles to determine the particle composition and size distribution. Most of the particles were found to be complex oxides containing Ti, Ce and Cr. Furthermore, the composition of the particles was found to change from a high Ce‐content to a high Cr‐content with longer holding time at 1600°C.     

Determination of the critical nucleus size of precipitates using the macroscopic composition gradient method

The critical minimum size of stable precipitate in the vicinity of the edge of miscibility gap is experimentally determined for Ni₃Al precipitate particles in the Ni-Al and Cu₄Ti particles in the Cu-Ti binary alloy systems using the macroscopic composition gradient method recently proposed. The results obtained are as follows: the critical nucleus size shows a rapid increase to several tens of nanometers in a very narrow composition region less than 0.3 at. pct from the phase boundary. Such a big critical size of the nucleus is statistically rationalized by the conventional nucleation theories, but remains kinetically unreasonable.     

Influence of alloying elements on the kinetics of strain-induced martensitic nucleation in low-alloy, multiphase high-strength steels

Low-alloy multiphase transformation-induced-plasticity (TRIP) steels offer excellent mechanical properties in terms of elongation and strength. This results from the complex synergy between the different phases, i.e., ferrite, bainite, and retained austenite. The precise knowledge of the austenite-to-martensite transformation kinetics is required to understand the behavior of TRIP steels in a wide array of applications. The parameters determining the stability of the metastable austenite were reviewed and investigated experimentally, with special attention paid to the effect of the chemical composition, the temperature, and the size of the austenite particles. The results show that the stability and rate of transformation of the austenite particles in TRIP steels have a pronounced composition dependence: austenite particles transform at a faster rate in CMnSi TRIP steel than in TRIP steels in which Si is fully or partially replaced by Al and P. The results clearly support the view that (1) both a high C content and a submicron size are required for the room-temperature stability of the austenite particles and (2) the effect of the chemical composition on the transformation is due to its influence on the intrinsic stacking-fault energy. In addition, the composition dependence of the Md ₃₀ temperature was derived by regression analysis of experimental data. The influence of the size of the retained austenite particles on their Ms ^σ temperature was studied by means of a thermodynamic model. Both the analysis of the transformation-kinetics data and the microstructural analysis by transmission electron microscopy revealed the very limited role of autocatalysis in the transformation.     

Simulation of Upward Seepage Flow in a Single Column of Spheres Using Discrete-Element Method with Fluid-Particle Interaction

The interaction between soil particles and pore water makes the behavior of saturated and unsaturated soil complex. In this note, upward seepage flow through a granular material was idealized using a one-column particle model. The motion of the individual particles was numerically simulated using the discrete-element method taking the interaction with the fluid into account. The fluid behavior was simulated by the Navier-Stokes equation using the semi-implicit method for pressure-linked equation. This approach has already been applied in powder engineering applications. However, there are very few studies that have used this approach in geotechnical engineering. This note first describes the qualitative and quantitative validation of this method for hydraulic gradients below the critical one by comparing the results with an analytical solution. Then, the ability of the method to simulate the macroscale behavior due to the interaction between particles and pore water at hydraulic gradients exceeding the critical hydraulic gradient is discussed.     

Dissolution of particles in binary alloys: part II. experimental investigation on an Al-Si alloy

A detailed experimental study of the dissolution kinetics of Si particles in an Al-Si alloy has been carried out in order to test the validity of the two models presented in the accompanying article.[1] In these models, the dissolution kinetics are dependent on the particle size distribution of the alloy. An alloy with composition C_o = 0.77 at. pct Si was heat-treated in order to obtain rather coarse spherical particles (1 to 10 μn). The size distribution of the particles was found to be close to the log-normal distribution. At high temperatures, when the solvus concentration was well above C_o, the experimental values were very close to the values of the model which predicted the highest dissolution rates. At lower temperatures, when the solvus concentration was closer toC _o, the experimental values lay in between the values predicted by the two models. The results clearly demonstrate that a size distribution of particles must be included in the model if an accurate prediction of the dissolution kinetics is to be achieved.     

Development of new grade of steel shots for casting cleaning

A technology has been developed for producing a new grade of steel shots used in casting cleaning. The developed technology is based on obtaining molten steel with the specified chemical composition microalloyed with titanium and using a highly efficient method of dispersing molten steel stream by water jet under high pressure followed by spheroidisation of produced particles and their solidification in water bath. The chemical composition and tapping temperature have been adjusted and different parameters of atomization process such as molten stream nozzle internal diameter, impact angle, water nozzle system and water pressure have been optimized to attain steel shots with the desired mechanical properties, microstructure, density and grain size. After drying, the steel shots are screened to different sizes. The desired grain size is then subjected to only one‐step tempering process. This technique reduces the processing steps (by omission of the reheating‐quenching treatment) and consequently gives significant savings in processing cost.     

Carbonitride precipitate growth in titanium/niobium microalloyed steels

Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) have been used to investigate the morphology, distribution, composition, particle size distributions, and growth kinetics of carbonitride precipitates in steels containing low levels of Ti, Nb, C, and N. During the aging, only the complex carbonitride precipitates of the form (Ti_xNb_1−x) (C_yN_1-y) were found in the newly nucleated and growing particles. The youngest of these particles which approach the size of critical nuclei tends to be Ti-rich. Almost all of these particles are nearly spherical. The initial growth of the precipitates, which is very rapid, lasts less than 30 seconds followed by slow ripening. A model predicting the growth kinetics of carbonitrides and composition variation within the precipitates for the initial stage (before coarsening) has been developed based on equilibrium thermodynamics with the inclusion of capillarity and multicomponent diffusional kinetics. Satisfactory agreement with the experimental results has been demonstrated.